This invention is concerned with improvements in or relating to the manufacture of shoes and is especially concerned with methods of attaching heels to shoes.
The term "shoe" where used herein is to be understood as referring to outer footwear generally whether complete or in the course of manufacture.
It is a common practice in the shoe industry to attach heels by means of nails which are hammered through the insole of the shoe into the heel. In most cases, if four or six nails are used, adequate attachment is obtained whether the heel is made of wood or of thermoplastic material. However, in the case of sharply tapering heels e.g. "stiletto" heels, which are generally made of thermoplastic material since wood is not sufficiently strong for this purpose, it may be very difficult to insert sufficient nails because of the limited fastening area available. The area available is limited by the taper of the heel which reduces the locality where there is sufficient depth of material for a nail to be inserted. (It is generally recommended that a heel-attaching nail be inserted to a depth of at least ten millimeters.) The attachment area available may well also be reduced by the presence of a shank in the shoe. Also, in the case of very high heels, whether or not they are of the "stiletto" type, it is difficult to achieve sufficiently strong attachment.